1. Field of the Invention
This invention relates to an actuator which synchronizes electrostatic adsorption with the vibration of a piezoelectric element to perform a step-driving operation.
2. Description of the Related Art
As digital cameras are mounted on cellular telephones and portable information devices, it is required to greatly reduce the size of photographic optical modules. In order to meet this requirement, an electrostatic actuator is proposed instead of the conventional electromagnetic actuator.
As one of the electrostatic actuators, an actuator which synchronizes electrostatic adsorption with the vibration of a piezoelectric element to perform a step-driving operation is known as is disclosed in U.S. Pat. No. 6,841,899, for example.
The step-driving actuator includes a substrate extended in a predetermined direction, a vibrating member supported on the substrate vibratably in the predetermined direction, a vibration generating portion configured to vibrate the vibrating member in the predetermined direction, a movable member having a first facing surface confronting the substrate and a second facing surface confronting the vibrating member, a movable electrode disposed at any one of the first facing surface and second facing surface of the movable member, and a counter electrode disposed on any one of the substrate and the vibrating member so as to confront the movable electrode. A potential difference is applied between the movable electrode and the counter electrode to cause an electrostatic force to act such that an apparent sliding resistance between the vibrating member and the movable member is greater than an apparent sliding resistance between the substrate and the movable member when displacing the vibrating member in a desired direction relatively on the substrate by vibrating in the predetermined direction, and thereby the movable member is relatively moved in the desired direction on the substrate.